As a USB (Universal Serial Bus) connectable flash memory card reader/writer, a USB storage type (based on the USB Mass Storage Class) is predominantly the mainstream, and there are hardly other types.
A USB connectable multi function device having the card reader/writer function and other functions (for example, a multi function device having a printer or scanner function) is also modeled after the stand-alone card reader/writer.
For this reason, in most models, the card reader/writer function is recognized by the PC (personal computer) as a USB storage type device.
Meanwhile, in a multi function device having the card reader/writer function, if an internal controller of a multi function device and a PC connected to the multi function device simultaneously access the memory card, many problems may occur.
Accordingly, in order to resolve these problems, JP-A-2004-94493 describes a technology that enables the internal controller of the multi function device and the PC connected to the multi function device to exclusively access the memory card.
However, if the access to the memory card is simply exclusively executed as described above, the memory card tends to be easily occupied by the PC for a comparatively long time. For this reason, the internal controller of the multi function device is liable to go into the situation that cannot access the memory card. Then, a user who frequently uses the multi function device as a stand-alone device may feel inconvenience of using the multi function device.
The reason why the PC occupies comparatively long time is that the PC and the internal controller of the multi function device access the memory card by different access methods. The details are as follows. First, an access from the PC to the memory card will be described. When accessing a file on the USB storage device, the PC accesses the memory card through a file system provided therein.
At this time, a request to access a physical storage area in the memory card (for example, a request to read data from the physical storage area or a request to write data to the physical storage area) is input from the PC to the multi function device. Meanwhile, no explicit notification indicating that the access from the PC to the memory card is completed is input from the file system provided in the PC.
Accordingly, the device can only guess that “if the PC does not access until a predetermined standby time elapses, the access from the PC is recognized as being completed”. As a result, for the standby time, the access authority to the memory card is wastefully occupied by the PC.
Next, an access from the internal controller of the multi function device will be described. The internal controller of the multi function device accesses the memory card through a file system provided in the device.
At this time, if the access to the memory card by the file system provided in the device is completed, the internal controller of the multi function device can immediately recognize that the access to the memory card is completed. In this case, therefore, unlike the access from the PC, the device does not need to stand by until the standby time elapses, and thus there is no case in which the internal controller of the multi function device wastefully occupies the access authority to the memory card.
In this case, it should not be interpreted that the access request from the PC is intentionally preferentially processed. In the event, however, due to the difference in the access method, the occupation time by the PC is likely to be extended, and the internal controller of the multi function device is likely to go into the situation that cannot access the memory card.